1. Field of the Invention
The present invention relates to a system for ground source cooling for refrigerant coolants. In particular, coolant for a refrigeration unit for a refrigerator or air conditioning unit is heated and requires an economical and effective cooling application. An appreciation of this need can be understood by review of a ground system's effects on air conditioning systems.
In air conditioning systems for residential use, a reversed cycle technique system is applied. A reversed cycle system receives heat from a colder body and delivers heat to a hotter body by virtue of a work input such as a compressor.
The reversed cycle is well-known through its uses in preserving foods, as well as conditioning air for summer and winter comfort. In a technical sense, a heat pump is a general name for all reversed cycles. A reversed cycle, as applied to a typical air conditioning application is the most common method of securing refrigeration. Heat is rejected at the higher temperature and added at the lower temperature The net work is: EQU W=Wont-Win=.intg.DQ=QA-.vertline.QR.vertline..
a negative number that indicates work is done on the system. The system is the circulating working substance, such as R-22 refrigerant, although the present invention is not limited to any one particular refrigerant as the present invention will work with all refrigerants. In the ideal case, all flow is without friction, except flow through the expansion valve, and all processes except those in the condenser and evaporator are adiabatic. In a reversed cycle, such as residential air condition or heat pumps, the state point conventionally moves in a counterclockwise sense on the TS plane, where T is temperature and S is total entropy.
In a simplified refrigeration cycle, starting at State 1, an isentropic compression brings temperature higher than the source temperature to T1 by an amount equal to .DELTA.T, so that heat can be rejected along an isothermal curve A. An isotropic expansion lowers the temperature to where heat may be added to the system reversibly from a cold room at T2+.DELTA.T. The refrigeration is represented by QA, and the net work to provide a set value of refrigeration for the system is depicted by W.
For a given temperature range and a particular isothermal curve A, the work must necessarily be the same as the equivalent power cycle, the heat rejected by the reversed cycle at the higher temperature must be equal to the heat added in the power cycle, and so on. The parameter used to indicate the efficiency of a reversed cycle is called the coefficient of performance, abbreviated COP and represented by the symbol .gamma.. For a reversed cycle used for cooling, the COP is stated as: ##EQU1## These values of the COP are the highest possible for all cycles operating between the temperatures T1 and T2. It is clear that the work W to activate and maintain the refrigeration cycle should be a minimum, since it must be manufactured and paid for. The basic tenets of this simple fact, which are the basis for modern thermodynamics are stated as follows:
1) The work REQUIRED will be reduced as the temperature T1 is lowered for refrigeration and T2 is raised for heating. In a refrigerating cycle, the lowest temperature T0 that is attainable by a natural coolant, such as the atmosphere, a lake, or an underground water table, is the most economical. In a heating cycle, the highest temperature T0 that is attainable by a natural coolant, such as the atmosphere, a lake, or an underground water table, is the most economical. In a refrigeration cycle, there is a natural lower limit for T1 set by T0. Likewise, there is an upper limit for T2 set by T0 for a heating cycle. In practice, T1 for refrigeration and T2 for heating is some 5.degree. to 20.degree. F. greater than T0. In a warming cycle, T2 must be some 10.degree.-20.degree. F. or more above the room temperature. Thus, if it is desired to keep a room at 70.degree. F., the refrigerant must stay at 90.degree. F. or more. Smaller temperature differences than mentioned could be used, but as the temperature difference decreases, the surface area needed in the heat exchanger increases in order to maintain the same rate of heat flow, thereby increasing the cost of the heat exchanger. In practice, it is a matter of getting an economical balance. For heating, the presence of relatively warm earth or ground water is very helpful. The earth or ground water provides natural sources of heat at temperatures higher than winter atmospheric temperatures. Likewise, for cooling, the presence of relatively cool earth or ground water is very helpful. The earth or ground water provides natural sources of cooling at temperatures lower than summer atmospheric temperatures. In a particular geographic location, we would tend to use the coldest convenient sink for cooling and the warmest convenient sink for heating. PA1 2) For particular temperature limits, the heat exchanger should take place at constant temperature for the most effective use of the work. In the case of vapor refrigerants, the refrigerant will be at a constant temperature during much of the heat transfer process.
2. Description of the Prior Art
Many air conditioning systems use water-cooled condensers. An evaporative condenser may be used to cool the condenser vapor. In this system, a conventional motor compressor, condenser, liquid receiver, drier, thermostatic expansion valve, and evaporator are used. The hot compressed refrigerant vapor is piped to the evaporative condenser. This part of the system is usually located on the roof or outside the building. In this mechanism, the water supply is piped to a holding tank. A float mechanism maintains a constant level of water in the tank. A water pump circulates and sprays water over the refrigeration condenser. A fan draws in air through the side of the evaporative condenser housing and forces it upward through the top. The water droplets are cooled by evaporation and then flow over the condenser. Some water is used up by the evaporative process. This is automatically replaced using a holding tank and a float mechanism. A pressure motor control is used on the refrigeration motor compressor in this instance.
Deficiencies in the evaporative condenser are the work required to drive the pump and fan, corrosion and scaling of heat exchanger equipment, cost and space requirements.
Many refrigeration and air conditioning systems have water-cooled condensers where tap water is circulated through them. Other applications use underground water. This water is then discharged into the sewer or a drainage ditch. Such an arrangement uses large amounts of water and is expensive and wasteful. Moreover, many places do not allow the use of tap water for cooling air conditioner condensers.
A cooling tower is another application of a water-cooled condenser. The cooled water is recirculated through the condenser and sometimes through the outer shell of the compressor. Some makeup water will be required to replace the water lost by evaporation. The cooling tower is a housing or shed into which air is drawn. It has a water spray arrangement and baffles. The sprayed water is exposed to the stream of air and becomes cool. A float mechanism connected to the water spray maintains a constant water level in the water reserve tank. The pump circulates the cooled water through the water-cooled refrigerant condenser.
Water is sometimes sprayed over the baffles. Cooling towers are available in a great range of sizes. Small ones may cool the water cooled condensers for home air conditioners.
Deficiencies in the cooling tower are the cost required to drive the pump and fan, corrosion and scaling of heat exchanger tubing, cost, and space requirements.
A water source heat pump uses a water-to-refrigerant heat exchanger to extract heat from a heat source. In residential settings, the source can be ground water, river or lake water, city water, stored solar energy, or the ground itself. In principle, water-source heat pumps have an efficiency advantage over air-source systems because of heat source temperature constancy. The annual range of variation in ground water or surface water temperatures in most parts of the country is much less than the variation in air temperature. In describing water-source heat pumps, it is important to distinguish between the equipment and the system in which the equipment is applied. Water-source heat pump equipment is either of the water-to-air or water-to-water type and is available in single package units or split systems that can be designed to accommodate a wide range of building types and heat sources. About 16 manufacturers make water-source heat pump equipment. A water source heat pump system can be either open-loop or closed-loop. Open-loop systems use ground water or surface water directly; water is pumped from the well, river, or lake through the water-to-refrigerant heat exchanger and, eventually, either returned to the source or pumped to a drainage basin, pond, or storm sewer. Closed-loop systems continuously circulate a heat transfer fluid, such as water or a water-antifreeze mixture, to extract heat from the ground or surface water source (and reject heat thereto). Water-source heat pump systems are most often classified according to the heat source utilized, the principal difference among these systems is the method employed for source-to-refrigerant heat exchange.
Ground water is available in most parts of the United States and many homes in rural areas have wells that tap into ground water. As mean ground water temperature maps show, the ground water, even in northern climates remains relatively moderate. Ground water heat pump systems are of the open-loop type. Water is withdrawn from a well, flows through the heat exchanger of the heat pump, where it exchanges heat with the refrigerant, and is then disposed of by reinjection or discharged. Single and multiple well systems are available. Deficiencies in the ground water heat pump systems are the regulations associated with removing and reinjecting ground water, the cost associated with drilling the well and pumping the water, and inefficient heat exchange between the water source and the refrigerant.
Ground-coupled heat pumps use the earth itself as a heat source and heat sink. The heat pump is coupled to the earth by means of a closed-loop heat exchanger, or ground coil, is usually either synthetic or copper piping and may be installed horizontally or vertically in the ground. The ground-coupled heat pump circulates water from the heat pump through the ground coil to absorb or reject heat. Apart from the heat exchanger configuration, ground-coupled heat pumps function similarly to open-loop water-source heat pumps. The closed-loop configuration eliminates the need for the great quantities of water demanded by open-loop water-source heat pumps. Also, water disposal is not required, thereby avoiding the need for a reinjection well. Ground-coupled heat pumps may apply to a wide range of homes, especially those with adequate space to install horizontal heat exchanger piping. Vertical heat exchanger systems are the only option for homes with small yards.
At present, all ground-coupled heat pumps use commercially available water-to-air equipment. Two basic configurations are used: the pressurized or closed-fluid system, and the atmospheric or open-fluid system. (This is not to be confused with the fact that a ground-coupled system is a closed-loop system, which means that the heat exchanger fluid recirculates within the heat pump and does not leave the system.) In what is termed an atmospheric system, the transfer fluid is exposed to atmospheric pressure, thus atmospheric systems typically require larger pumps to accommodate pressure head differences. Pressurized systems, whose transfer fluids are not exposed to atmospheric pressure, require smaller circulation pumps and, as a result, have lower operating costs. Pumping power may account for 10 to 12% of total electrical consumption in an atmospheric system, and 4 to 5% in a pressurized system. Consequently, the performance of the atmospheric system will be somewhat lower than that of the pressurized system. (Atmospheric or pressurized classification may be applied to all water-source heat pump systems. The most common ground-coupled heat exchangers are horizontal serpentine, vertical U-tube, and vertical U-tube in multiple shallow wells. Some concentric tube designs have been experimented with, but are uncommon. Heat exchangers are installed either horizontally or in a vertical well hole, and typically are constructed on-site.
The efficiency of the common air-to-air heat pump depends greatly on outdoor temperature. To improve this efficiency, some installations use a coil buried in the ground beneath the frost level, rather than a coil in the atmosphere. If the coil is buried at some depth and a long enough coil is used, the efficiency of the heat pump may be very good.
On the heating cycle, liquid refrigerant flows though a refrigerant control and into the ground coil. Since the refrigerant in the ground coil is under low pressure, it boils, absorbing heat from the ground surrounding the coil. The vaporized refrigerant is then drawn into the compressor. It is compressed and discharged into the condenser, which, in this case, is the heating coil for the heating system. The condenser changes the vaporized refrigerant to a liquid. The refrigerant gives up its heat to the room air. The liquid refrigerant returns to the refrigerant control to repeat the cycle.
The same mechanism is used to cool in summer. The cycle is reversed to move heat from the building to the outdoors. In this case, the inside coil serves as the evaporator and the ground coil becomes the condenser. The ground absorbs the heat from the vaporized refrigerant. Heat pump installations using ground sources are even more efficient if the ground coil is placed in a spring or in a flowing well with water at about 50.degree. F. Some heat pump installations have been successful using a coil placed in the bottom of a lake.
Although designs have been devised in which the heat pump's refrigerant is pumped through a direct refrigerant expansion coil buried in the ground, the current state of technology has led heat pump manufacturers to recommend not using this technique. Considerations include cost due to two factors: necessary custom design of the heat exchanger, and use of copper as the coil material. The heat exchanger must be custom-designed by a refrigeration engineer to ensure the oil return rate to the compressor is adequate and occurs under all operating conditions. Additionally, cost is a consideration, due to the fact that in most installations, the air condensing unit is completely replaced with a buried coil. This leads to high installation expenses. Copper's durability makes it the only heat exchanger material that can be used. Horizontal burial is preferred if a DX coil is used because of oil return problems. The advantage of using the heat pump refrigerant as the heat exchanger working fluid is that it eliminates the temperature drop that typically occurs between the refrigerant and the heat exchanger fluid. The performance of the DX ground-coupled heat pump may be 20% higher than that of systems using other heat exchanger fluids.
The present invention relates in general to a method and apparatus for augmenting exiting refrigeration systems to provide refrigerant liquid line subcooling by using ground source cooling.